1. Field of the Invention
The present invention relates to an expanding gas-operated setting tool for driving fastening elements, such as nails, bolts, pins and the like in a substrate and including a housing, a setting mechanism located in the housing, and a source of expanding gases, e.g., a fuel reservoir.
2. Description of the Prior Art
Setting tools of the type described above generally also includes electronic components, such as electronically controlled valves, ignition devices, ventilators, etc. These components and their control devices must be supplied with power, preferably not dependent on an electrical network or another centralized power system.
U.S. Pat. No. 4,403,722 discloses a gas-driven setting tool for which the mixture of air and fuel in the combustion space is homogenized before ignition by an electrically driven ventilator. A nickel-cadmium battery is provided there for supplying power to the ventilator driving mechanism and its control device.
The technologically limited capacity of the nickel-cadmium battery is a major disadvantage of this type of power supply.
Usable alternative batteries with better efficiencies (capacity/weight) cannot be employed in practice. A NiMH battery with, for example, a higher capacity at the same weight, cannot be used at temperatures below 0xc2x0 C., since the voltage behavior of this battery is not stable at cold temperatures.
Furthermore, U.S. Pat. No. 6,123,241 discloses a gas-driven setting tool in which various electronic devices are controlled and/or monitored by an extensive electronic control system. Thus, there provided on the setting tool various sensors, such as temperature, pressure and working-surface temperature sensors as well as an electronic ignition and an electrically driven. Two sources of power are required to supply this setting tool. An alkaline battery supplies electrical energy to a microprocessor, which is the core of the control system, and a lead acid battery is the main battery. It is a disadvantage of this setting tool that, due to the high demand for electric energy, two batteries are used there to supply power. Consequently, the size and weight of the tool are larger.
It is, therefore, an object of the invention to provide a setting tool of the aforementioned type, which can be operated independently of its location and which avoids the aforementioned disadvantages.
This and other objects of the present invention, which will become apparent hereinafter, are achieved by using, as a power source, a fuel cell operable by fuel, stored in a fuel reservoir provided on the tool, and oxygen. Preferably, the reservoir can be refilled or, when empty, exchanged for a full reservoir. The oxygen can also be obtained from a reservoir provided on the setting tool or taken from the surrounding air.
By using a fuel cell in the setting tool, a very high efficiency of up to 60% which is independent of any mains supply, and a long operating time can be achieved advantageously with one filling of the fuel reservoir. Furthermore, the fuel cell, as a source of electric energy, enables to use the setting tool even at temperatures below 0xc2x0 C. It is also possible to operate the setting tool for the same length of time as at higher temperatures. This is usually not the case with batteries.
When a setting tool is operated with liquid or gaseous fuels, advantageously, the fuel cell is coupled thermally to the fuel reservoir or the fuel can. The thermal coupling can be accomplished, for example, by arranging the fuel cell adjacent to the fuel reservoir, so that the latter is heated by the waste heat coming from the fuel cell. Dependent on the type of the fuel cell, the entropy or heat of reaction can be up to 90xc2x0 C.
Due to this measure, the fuel can or reservoir, which is still cold at the start of the operation, can be heated rapidly and, when the ambient air is cold, so that interruptions in the supply of fuel to the tool can be avoided. In particular, the danger of vapor locks in setting tool, operated with liquefied gas, is reduced, and the ignition behavior above a pre-set operating temperature is improved.
Advantageously, the fuel cell and the fuel reservoir can be disposed jointly in a heat-conducting part of the setting tool. The fuel cell and the fuel reservoir can also be accommodated separately in the heat-conducting part. By such a measure, uniform heating of the fuel reservoir is achieved. The heat-conducting part may also be an integral component of the metal housing of the setting tool.
Advantageously, means for cooling the heat-conducting part, such as cooling ribs or housing ribs, over which the excess thermal energy, for example, when the fuel can is already heated, can be released into the surrounding air, may be provided at the heat-conducting part.
When a PEM fuel cell (polymer electrolyte membrane fuel cell) or a similar fuel cell is used, the advantages are, for example, the uncomplicated handling, the low weight and the high power density because of the good proton conductivity of the electrolyte.
The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to its construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiments, when read with reference to the accompanying drawings.